1. Field of the Invention
The invention relates to a process and an apparatus for the drying, more in particularly the drying of fine grain solid particles in a fluidized bed.
2. Description of the Prior Art
West German Pat. No. 19 10 003 or West German Auslegeschrift 26 22 565 show centrifugal moving bed or fluidized bed dryers, in which the solid particles to be held in suspension are introduced from above or below into a screening drum.
In order to insure that all of the solid particles introduced into the turbulent layer forming the fluid bed are maintained in suspension by the carrier flow of gas, a suitable grain size distribution must be present. This is to prevent appreciable proportions of the solid particles remaining on the surface of the screening drum or being carried out in the radially inward direction from the turbulent layer by a carrier gas stream. This condition is part of a technical problem which in most cases cannot be corrected at a justifiable cost.
Numerous wet products to be dried in a fluid bed tend to agglomerate. The agglomerates then behave in the manner of coarse particles and as a result of their unfavorable fluidizing behavior can no longer be retained in the turbulent layer by the flow of gas, whereupon they sediment on the surface of the screening drum where they gradually form a deposit capable of clogging the orifices of the screening drum and thereby stopping the continuous process.
A further effect interfering with or preventing the normal operation of the process occurs when a very finely grained wet product to be dried is introduced into the screening drum. Due to the presence of strong interparticle adhesion forces, which cannot be overcome by the forces of the flow in the gravity field of the earth, so-called canals are formed, through which the carrier gas stream passes ineffectively, without fluidizing the solid particles in the area affected.